(Henry Spencer) wrote:
It's virtually certain that the surface itself is sterile, and that
terrestrial organisms released on it will die.
[...]
It's likely that the immediate subsurface is the same way, but that has
not yet been confirmed, and needs to be.

This press release from 2003 claims that bacteria in their endospore
forms might survive at depths below 5mm for a while at least.

http://www.biomedcentral.com/info/ab...es?pr=20030403